The present invention relates to the coding and decoding of data, such as map data that indicate the distribution of first and second data segments in a transmitted data field.
The ATSC digital television standard presently provides for the transmission of successive data fields each comprising 313 segments extending over a 24.2 ms time interval. FIG. 1 discloses an exemplary format for a data field according to this standard. The first segment of each field is a field sync segment. The field sync segment is composed of four two-level segment sync symbols and space for 828 other two-level symbols. A portion of this space is used for a field sync, and another portion of this field is reserved. Except for the reserved portion, the information in the frame sync segment does not change from field to field. Each of the remaining segments of each field comprises four two-level segment sync symbols and 828 n-level data symbols where n is currently eight, although n could be other integers such as two, four, sixteen, etc. Except for the segment sync portion, it is highly likely that the data in the remaining segments of the fields change from field to field.
As indicated by U.S. patent application Ser. No. 09/804,262 filed on Mar. 13, 2001, there is presently some interest in extending the ATSC digital television standard to allow a field to contain a mix of more robustly coded data (referred to herein as E-VSB data) and the data currently provided for in the standard (referred to herein as VSB data). Preferably, the data mix is employed on a segment-by-segment basis such that some segments of a field are used to transmit VSB data exclusively and the remaining segments of the field are used to transmit E-VSB segments exclusively. However, it is possible that all data segments of a field could contain either E-VSB data segments exclusively or VSB data segments exclusively. Moreover, it is also possible that the E-VSB data contained in some segments of a field may be coded with one robust coding rate and that the E-VSB data in other segments of the field may be coded at other robust coding rates.
As disclosed in the above mentioned ""262 application, a map that indicates which segments contain the more robust (E-VSB) data and which segments contain standard VSB data is preferably provided by the transmitter to the receiver so that the receiver can properly decode and otherwise process the received VSB and E-VSB data. Assuming that a field contains E-VSB data at different coding rates, the map in that case must also designate the coding rates that apply to the differently coded E-VSB data segments.
The ""262 application describes one mapping system. Co-pending U.S. patent application Ser. No. 10/011,900 filed Dec. 3, 2001 as well as the ""333 application describe another mapping system that reliably identifies which segments contain first data (such as VSB data) and which segments contain second data (such as E-VSB data).
Multipath distortion, commonly found on terrestrial television channels, can affect the ability of the receiver to properly receive and process the map. For example, in the case of map data transmitted in the reserved portion of the field sync segment, data that tends to be random from field to field will be superimposed on the map data if a ghost is a long ghost such that it occurs in the data of a data segment rather than in the field sync segment. If the map and its duplicate are transmitted in two successive field sync segments, the map and its duplicate add with a high degree of correlation when a map and its duplicate are averaged in a receiver, but the superimposed data add with a much lower degree of correlation. Thus, the map is more easily distinguished from the data. Accordingly, the map is readily detectable.
On the other hand, if the ghost is a short ghost such that it occurs in the frame sync segment of a field, frame sync symbols that may not vary from field to field are superimposed on both the map and the duplicate. Accordingly, while the map and its duplicate add with a high degree of correlation, the superimposed field sync symbols also add with a high degree of correlation. Thus, the map cannot be easily distinguished from the field sync symbols. Accordingly, the map is difficult to detect.
The present invention, in one of its embodiments, allows maps to be more easily detected even in the presence of a short ghost.
In accordance with one aspect of the present invention, a data receiving method comprises the following: receiving a map, wherein the map designates locations of first and second data in a field; receiving a duplicate of the map, wherein at least one of the map and the duplicate is scrambled so that the map and the duplicate have different sequences relative to one another; de-scrambling the scrambled map and/or duplicate; processing the unscrambled versions of the map and the duplicate to produce a map output; and, separating the first and second data according to the map output.
In accordance with another aspect of the present invention, a method is provided to format first and second data for transmission in successive alternating odd and even data fields, where each data field comprising a sync segment and a plurality of data segments. The method comprises the following: providing an odd field map data unit Ao, Bo, Co and an even field map data unit Ae, Be, Ce defining the mix of data segments containing only first data and data segments containing only second data for each respective odd and even data field, each of the components A, B and C of the map data units comprising n bits; encoding each of the map data unit portions AoBo, CoAe and BeCe to form vectors AoBoP1, CoAeP2 and BeCeP3, where each of P1, P2 and P3 comprise 2n parity bits; bit-wise scrambling each of the vectors AoBoP1, CoAeP2, and BeCeP3 to produce a corresponding scrambled vector and providing a stream of alternating ones of the unscrambled and corresponding scrambled vectors; convolutionally interleaving the stream of vectors; inserting successive 12n bits of the convolutionally interleaved vectors for transmission in corresponding predefined portions of the sync segments of a plurality of successive alternating odd and even data fields; and, formatting each successive pair of odd and even data fields for transmission after insertion in the sync segments of the interleaved bits of the unscrambled and scrambled vectors defining the mix of data segments for the respective pair of odd and even data fields.
In accordance with yet another aspect of the present invention, a method is provided to recover first and second data from successive alternating odd and even data fields. Each data field comprises a sync segment and a plurality of data segments. An odd field map data unit Ao, Bo, Co and an even field map data unit Ae, Be, Ce define the mix of data segments containing only first data and data segments containing only second data for each respective odd and even data field. Each of the components A, B and C of the map data units comprises n bits, and each of the map data unit portions AoBo, CoAe and BeCe is encoded to form corresponding vectors AoBoP1, CoAeP2 and BeCeP3. Each of P1, P2 and P3 comprise 2n parity bits, and each of the vectors AoBoP1, CoAeP2, and BeCeP3 is bit-wise scrambled. The un-scrambled vectors and the scrambled vectors are convolutionally interleaved, and successive 12n bits of the convolutionally interleaved vectors are contained in corresponding predefined portions of the sync segments of a plurality of received successive alternating odd and even data fields. The method comprises the following: receiving the alternating odd and even fields; convolutionally de-interleaving the unscrambled and scrambled vectors; de-scrambling the de-interleaved scrambled vectors; processing corresponding ones of the de-interleaved vectors and the de-interleaved and de-scrambled vectors to produce output vectors; decoding the output vectors; and, separating the first and second data according to the decoded vectors.
In accordance with still another aspect of the present invention, a method is provided to format first and second data for transmission in successive alternating odd and even data fields, where each data field comprises a sync segment and a plurality of data segments. The method comprises the following: providing an odd field map data unit Ao, Bo, Co and an even field map data unit Ae, Be, Ce defining the mix of data segments containing only first data and data segments containing only second data for each respective odd and even data field, each of the components A, B and C of the map data units comprising n bits; encoding each of the map data unit portions AoBo, CoAe and BeCe to form vectors AoBoP1, CoAeP2 and BeCeP3, where each of P1, P2 and P3 comprise 2n parity bits; providing a duplicate of each of the vectors AoBoP1, CoAeP2, and BeCeP3 to produce a corresponding duplicate vector and providing a stream of alternating ones of vectors and duplicate vectors; convolutionally interleaving the stream of vectors and duplicate vectors; inserting successive 12n bits of the convolutionally interleaved vectors for transmission in corresponding predefined portions of the sync segments of a plurality of successive alternating odd and even data fields; and, formatting each successive pair of odd and even data fields for transmission after insertion in the sync segments of the interleaved bits of the vectors and duplicate vectors defining the mix of data segments for the respective pair of odd and even data fields.
In accordance with a further aspect of the present invention, a method is provided to recover first and second data from successive alternating odd and even data fields, where each data field comprises a sync segment and a plurality of data segments. An odd field map data unit Ao, Bo, Co and an even field map data unit Ae, Be, Ce define the mix of data segments containing only first data and data segments containing only second data for each respective odd and even data field. Each of the components A, B and C of the map data units comprises n bits Each of the map data unit portions AoBo, CoAe and BeCe is encoded to form corresponding vectors AoBoP1, CoAeP2 and BeCeP3, each of P1, P2 and P3 comprise 2n parity bits, and each of the vectors AoBoP1, CoAeP2, and BeCeP3 is duplicated. The vectors and the duplicate vectors are convolutionally interleaved, and successive 12n bits of the convolutionally interleaved vectors are contained in corresponding predefined portions of the sync segments of a plurality of received successive alternating odd and even data fields. The method comprises the following: receiving the alternating odd and even fields; convolutionally de-interleaving the vectors and duplicate vectors; processing corresponding ones of the de-interleaved vectors and the de-interleaved duplicate vectors to produce output vectors; decoding the output vectors; and, separating the first and second data according to the decoded vectors.